The overall objectives of this project are to identify proteins which regulate and/or participate in DNA replication or repair using the Novikoff hepatoma as a model system for eukaryotic DNA synthesis. The DNA polymerases have been purified and used to screen for proteins which stimulate the in vitro reaction. Eight different factors have been identified to date and purified to varying degrees, several to homogeneity. Each factor is being characterized as an individual protein and in its interactions with the polymerase in an attempt to establish its role in DNA synthesis in vivo.